The rolling-type motion guide device, which comprises a guide mechanism in which rolling elements are incorporated as an inclusion, is advantageous in that its motion is smoother than that of a sliding-type motion guide device. For this reason, the rolling-type motion guide device has been used in a wide variety of applications such as machine tools, semiconductor/liquid display manufacturing apparatuses, and robots. One example of use of such a rolling-type motion guide device is shown in FIG. 15, in which the device is used at the Z-axis of a vertical machining center. In this example, a motion guide device 22 is able to guide the linear motion of a driver 24 along the Z-axis relative to a base 23, in which the driver 24 rotates a machine tool 21.
However, when the rolling-type motion guide device 22 is used for the Z-axis of this kind of machining center, there may occur vibration at the motion guide device 22 during the machining operation. This vibration, if occurring, is magnified at the machine tool 21 located at the distal end of the driver 24, which gives rise to a problem of poor surface-machining accuracy. For the machine tool 21, the vibration forces the machine tool 21 to strongly touch the workpiece surface, thus bringing about a problem that the lifetime of the machine tool 21 is reduced. To cope with these problems, instead of the rolling-type motion guide device, a sliding-type motion guide device is sometimes used which provides higher damping performance.
As a matter of course, use of the sliding-type motion guide device cannot enjoy the merit of gaining smoother motions given by the rolling-type motion guide device. In order to improve the damping performance while still keeping the greatest benefit of smoother motions of the rolling-type motion guide device, there has been known a technique shown in FIG. 16, in which a squeeze film damper 27 is formed between a raceway rail 25 and a moving block 26 such that the squeeze film damper 27 damps the moving block from vibrating (refer to Patent Reference 1, the second page). According to the fluid damping technique using this squeeze film damper 27, the moving block 26 has formed thereon a first sliding surface 28 facing an upper surface of the raceway rail 1 and a second sliding surface 29 facing a lower surface of a swelled wall of the raceway rail 1. Between the first and second sliding surfaces 28 and 29 and the raceway rail 1, a gap t of several tens of micrometers (μm) or thereabouts is formed and fully charged with oil, which functions as the squeeze film damper.    [Patent Reference 1] Japanese Patent Laid-open Publication No. 5-60129.
In the fluid damping technique using the squeeze film damper 27, resistance occurs when the moving block vibrates in the axial direction of the raceway rail so that the vibration in the axial direction of the moving block can be damped. However, this technique is not effective for damping the vibration of the moving block in the direction perpendicular to the axial direction. The present inventors have found that vibration resulting in a problem of the motion guide device applied to the Z-axis of the machining center is vibration generated in the perpendicular direction to the axial direction of the raceway rail. The vibration in the direction perpendicular to the axial direction is generated when a workpiece is under machining work and the moving block is stopped or moving at slower speeds. The problematic vibration is generated due to the fact that the rolling elements behave like a spring.